After years of contamination and decreasing output, China's Miyun Reservoir is rebounding, say researchers from China and the U.S. Rice farming had contaminated and tapped the reservoir, which lies 100 miles north of Beijing and is the main water source for the city's 20 million inhabitants. But four years ago, the Chinese government began paying farmers to grow corn instead, which requires less water and leads to less fertilizer and sediment runoff than rice farming. Now, water quality tests show that fertilizer runoff declined sharply, the researchers found, and the amount of reservoir water available to Beijing and surrounding areas has increased. Farmers also made more money growing corn instead of rice and were able to spend less time tending their crops, the study concluded.